As a variable displacement compressor provided in a refrigeration circuit of an air conditioning system for vehicles, etc., a compressor such as one disclosed in JP-A-2000-18172 is known. As depicted in FIG. 3, this variable displacement compressor 50 has a cylinder block 51 with a plurality of cylinder bores 51a, a front housing 52 provided at one end of cylinder block 51, and a rear housing 53 provided to cylinder block 51 via a valve plate device 54. A compressor main shaft 56 is provided as a drive shaft across a crank chamber 55 formed by cylinder block 51 and front housing 52, and an inclined plate 57 is disposed around a central portion of the compressor main shaft. Inclined plate 57 connects a rotor 58 fixed to compressor main shaft 56 and a connecting portion 59.
One end of compressor main shaft 56 extends to an outside through a boss 52a protruded toward an outside of front housing 52, and an electromagnetic clutch 70 is provided around the boss 52a via a bearing 60. Electromagnetic clutch 70 comprises a rotor 71 provided around boss 52a, a magnet unit 72 contained in the rotor, and a clutch plate 73 provided on one outer end surface of the rotor. One end of compressor main shaft 56 is connected to clutch plate 73 via a fastener 74 such as a bolt. A seal member 52b is inserted between compressor main shaft 56 and boss 52a, thereby isolating between the inside and the outside. Further, the other end of compressor main shaft 56 is present in cylinder block 51, and it is supported by a supporting member 78. Where, labels 75, 76 and 77 indicate bearings, respectively.
A piston 62 is inserted free to be slid into cylinder bore 51a. The periphery of inclined plate 57 is disposed in a recessed portion 62a formed at the inside of one end of piston 62, and by forming a structure for engaging piston 62 and inclined plate 57 to each other via a pair of shoes 63, the rotational movement of inclined plate 57 is transformed into the reciprocating movement of piston 62.
A suction chamber 65 and a discharge chamber 64 are formed in rear housing 53 separately from each other. Suction chamber 65 can communicate with cylinder bore 51a via a suction port 81 provided on valve plate device 54 and a suction valve (not shown), and discharge chamber 64 can communicate with cylinder bore 51a via a discharge port 82 provided on valve plate device 54 and a discharge valve (not shown). Suction chamber 65 communicates with crank chamber 55 via a gas chamber 84 formed at a shaft end extended portion of compressor main shaft 56, through an opening 83 (a fixed orifice).
A displacement control valve 10 is provided in a recessed portion of a rear wall of rear housing 53 in this variable displacement compressor 50. As depicted in FIG. 4, displacement control valve 10 is provided in a containing portion 53a for a control mechanism, which is formed as a recessed portion at one end of the inside of rear housing 53. Displacement control valve 10 has a valve casing 1 comprising a valve casing body 1a and a cap member 1b provided at one end of the valve casing body. A bellows 2 is disposed as a pressure sensing means in a pressure sensing space formed at one end of valve casing 1. Bellows 2 comprises a bellows body 2b, shaft members 2d protruded inward from both ends of bellows body 2b so that the tips thereof are spacedly separated, an inside spring 2a disposed in bellows body 2b, and a supporting member 2c provided at one end of bellows body 2b continuously from one end of one shaft member 2d, and the inside of bellows body 2b is set substantially at a vacuum condition. Further, a spring 3 is disposed around supporting member 2c so as to press bellows body 2b downward in the figure via shaft member 2d. This bellows 2 functions as a pressure sensing means for receiving a pressure of suction chamber 65.
A rod guiding hole 1c is provided in casing body 1a through the displacement control valve in its axial direction. A pressure sensing rod 4 is inserted into rod guiding hole 1c of casing body 1a and supported by casing body 1a at a condition where one end of the rod is brought into contact with the upper end of supporting member 2c of bellows 2. A valve body 5a formed as a large diameter portion at one end of valve mechanism 5 is brought into contact with the other end of pressure sensing rod 4. Because bellows 2 and pressure sensing rod 4 as a pressure sensing means are operationally connected to each other, valve body 5a opens/closes communication passageways 66, 1g, 1d, 1e and 68 between discharge chamber 64 and crank chamber 55 in response to expansion of bellows 2. A fixed iron core 7 provided on the upper end of casing body 1a at a contact condition for slidably supporting valve shaft 5b of valve body 5a is disposed around valve mechanism 5, accompanied with rod guiding hole 7a, and a valve chamber 6 is formed by casing body 1a and one end portion of fixed iron core 7.
Valve chamber 6 communicates with discharge chamber 64 through a communication passageway 68, a space 14 and a communication passageway 1e. Further, a plunger 9 is provided on the other end of fixed iron core 7, and a tube 8 is provided so as to cover plunger 9 together with fixed iron core 7. A plunger chamber 11 is defined by fixed iron core 7 and tube 8. A communication passageway 13 is provided so as to communicate between plunger chamber 11 and suction chamber 65 via a communication passageway 67, a hole 1f and pressure sensing space 15. An electromagnetic coil comprising a solenoid 12 as means for applying a magnetic field, which acts an electromagnetic force to a gap between plunger 9 and fixed iron core 7 and acts the electromagnetic force to valve body 5a via a valve shaft 5b (a solenoid rod), is provided on the outer circumferential surface of tube 8.
Using the displacement control valve mechanism 10 thus constructed, a displacement for discharge is changed by adjusting an opening degree of a control passageway connecting between a discharge pressure region and a control pressure region (that is, a crank chamber pressure region).
In the above-described variable displacement compressor 50, the discharge pressure supply passageway from discharge chamber 64 to crank chamber 55 is formed by communication passageways 68, 1e, 1g and 66, and the pressure relief passageway from crank chamber 55 to suction chamber 65 is formed by the gap between compressor main shaft 56 and bearing 77, gas chamber 84 and fixed orifice 83. In these discharge pressure supply passageway and pressure relief passageway, the flow of the gas supplied from discharge chamber 64 always becomes a one-way flow of discharge chamber 64→displacement control valve 10→crank chamber 55→gas chamber 84 →fixed orifice 83→suction chamber 65. In such a passageway structure wherein only a one-way flow occurs, for example, when the gas flow speed is in a low-flow speed range, on the way of the passageway, for example, at a position of bearing 77 or shaft supporting member 78 or a vicinity thereof, the flow is liable to stagnate, and accompanying with it, foreign matters in the gas are liable to accumulate. Such a foreign matter accumulation may cause an abrasion of, in particular, bearing 77 or compressor main shaft 56, and may damage the reliability of the compressor.
Further, in the above-described variable displacement compressor 50, because two communication passageways of the discharge pressure supply passageway from discharge chamber 64 to crank chamber 55 and the pressure relief passageway from crank chamber 55 to suction chamber 65 are necessary, the processing of cylinder block 51 may become complicated.